1. Field of the Invention:
The present invention relates to a semiconductor memory device, and more particularly a multi-port memory device suitable for application to the video field.
2. Description of the Related Art:
A dual port memory device equipped with a random access port and a serial output port has been used as a video memory for storing image or video data. An example of the dual port memory device is disclosed in U.S. Pat. specification No. 4,633,441 issued to Ishimoto. The conventional dual port memory device is constructed as follows. A plurality of memory cells are arranged in a matrix form of rows and columns and one row of memory cells are read out at a time in parallel. The random access port selects one of the selected row of memory cells for read out or write in while the serial access port has a data register for storing data read from the selected row of memory cells and a serial read circuit for serially reading data stored in the data register one by one. Thus, in the conventional dual port memory device, data can be processed through the random access port while data can be serially accessed through the serial access port.
However, when the conventional dual port memory device is used as an image memory, it is not possible, for example to input a television image into the memory and to output image data on the real time basis to a CRT display while television image is being processed. Thus, in the conventional dual port memory, it is impossible to perform serial read and serial write operations simultaneously.